Various types of telecommunication systems for interconnecting telephone communication trunks to a transmission network are known in the patent literature and in the marketplace. One type of such apparatus is known as Digital Circuit Multiplication Equipment systems which typically include Time Assignment Speech Interpolation (TASI) Apparatus. There is described in applicant's European Patent and in applicant's U.S. Pat. No. 4,523,309, TASI apparatus which has gained widespread market acceptance.
A particular feature of the abovementioned U.S. Pat. No. 4,523,309 is that control information such as the assignment, synchronization and identification information is transmitted along the communication channels instead of on separate signaling channels as in the prior art. In addition, the signaling communication channel assignment information is also supplied via the voice channels rather than via the signaling channels.
Another type of telecommunication system for interconnecting telephone communication trunks to a transmission network is described in a paper by R. W. Muise et al entitled "Experiments in Wideband Packet Technology," given at the International Zurich Seminar on Digital Communication, April, 1986. The paper discloses a system which comprises an access interface and a wideband packet switch for sending packets of speech and data across a transmission network.
There are known Digital Circuit Multiplication Equipment (DCME) systems in which the advantages of Digital Speech Interpolation (DSI) and adaptive pulse code modulation (ADPCM) compression techniques have been incorporated, as demonstrated in applicant's U.S. Pat. No. 4,747,096 which also uses voice channels for the transmission of control information. In addition, the system detects voiceband data transmission and compresses it according to an optimal ADPCM adapted for voiceband data.
However, the optimal ADPCM adapted for voiceband data compresses the voiceband data at a 2:1 rate whereas the compression rate of the DSI and the ADPCM for speech is 6:1. Thus, with the current proliferation of personal facsimile machines whose signals when transmitted via a DCME are compressed as voiceband data, the overall compression rate of a DCME is approaching 3:1.
In a Delayed Contribution D.788/XVIII presented at the CCITT Working Party XVIII/8 in Geneva Switzerland on Jul. 8-15, 1986 by EUTELSAT entitled "EUTELSAT Considerations on LRE-DSI characteristics for Digital Circuit Multiplication", there appears a proposal to demodulate V.29 voice band data signals in order to enable such signals to be transmitted via a compression system which employs ADPCM encoding for signal compression. This reference only proposes V 29 modem demodulation in DCME but does not explain how to do it. Importantly, it does not teach how to detect facsimile signals for subsequent demodulation thereof.
In a Final Report submitted to the International Maritime Satellite Organization (INMARSAT) entitled "Study of Facsimile Interface Units for Future Inmarsat Digital Communications System" dated Jul. 28, 1988 there is proposed a concept for demodulation of an all-facsimile channel. No consideration is given to detection of facsimile signals on a "mixed" channel which carries both speech and facsimile signals, and switching between different processing routes for facsimile and speech in response to such detection. Furthermore, this reference does not deal with many facsimile protocols which are in common use in such "mixed" channels.